PURPOSE: To securely suppress unnecessary frequency components by generating an (n)-fold frequency signal from an intermediate frequency signal, adjusting the phase and amplitude of the generated signal and combining it together with the intermediate frequency signal, and converting the frequency of the composite signal with a local oscillation frequency signal.

CONSTITUTION: A signal processing part 6 generates the signal of frequency nfIF which is (n) times as high as an intermediate frequency fIF from the signal of intermediate frequency fIF by an (n)-fold wave generation part 2. Then a phase adjustment part 3 adjusts the phase and an amplitude adjustment part 4 adjusts the amplitude. Then a composition part 5 composes one signal of the phase and amplitude adjusted signal of frequency nfIF and the signal of intermediate frequency fIF. A frequency conversion part 1 imposes frequency modulation upon the output signal of the composition part 5 with the signal of local frequency fLO from a local oscillator. Thus, a signal of radio frequency fLO±fIF from which unnecessary components due to cross modulation distortion between the signal of local frequency fLO and the signal of intermediate frequency fIF are removed can be obtained.